Physics

Weight

Weight is a force caused by gravity. The weight of an object is the gravitational force between the object and the Earth. The more mass the object has the greater its weight will be.Weight is a force, so it's measured in newtons. On the surface of the Earth an object with a mass of 1 kg has a weight of about 10 N.

What are forces?

A force are be a push, pull and twist. For example, when you push open a door you have to apply a force to the door. You also have to apply a force to pull open a drawer. And to twist a tap for example.

Gravity

All objects have a force that attracts them towards each other. This is called gravity. Even you attract other objects to you because of gravity, but you have too little mass for the force to be very strong. Gravitational force increases when: The masses are bigger. The objects are closer.

Mass and weight

Remember that mass is measured in kilograms, kg, and weight is measured in newtons, N.The mass of an object stays the same wherever it is, but its weight can change. This happens if the object goes somewhere where gravity is stronger, or weaker, such as the Moon.The Moon has less mass than the Earth, so its gravity is less than the Earth's gravity. This means that objects weigh less on the Moon than they do on the Earth.The Moon's gravity is one sixth of the Earth's gravity. A 120 kg astronaut weighs 1200 N on Earth. On the Moon they would weigh only 200 N. The astronaut's mass is 120kg wherever they are.

You need to know!!

Remember: a mass of 1 kg has a weight of about 10 N on Earth.

Mass

The mass of an object is the amount of matter or "stuff" it contains. The more matter an object contains, the greater its mass. An elephant contains more matter than a mouse, so it has a greater mass. Mass is measured in kilograms, kg, or grams, g.A 100 kg object has a greater mass than a 5 kg object. Remember an object's mass stays the same wherever it is.

Frictional forces

Whenever an object moves against another object, it feels frictional forces. These forces act in the opposite direction to the movement. Friction makes it harder for things to move.